1. Field of the Invention
The present invention relates to an isolator/circulator which can be used for the component's protection and impedance matching of a system and terminal in a transport communication system, a personal communication system, CT (Cordless Telephone) and satellite communication systems and, more particularly, to a microstripline/stripline isolator/circulator with a propeller-type resonator.
2. Description of the Prior Art
Recently, it has been required that a isolator/circulator to be reduced in size, weight and manufacturing costs due to the miniaturization of transport communication systems, satellite communication systems and millimeter wave. Desirable characteristics include a low insertion loss, a high isolation and a wide bandwidth.
Generally, an "isolator" passing a propagation in the forward direction without attenuation is a device for absorbing a propagation in the reverse direction, a "circulator" is a circuit device circulatory arranged between terminals for input and output thereof. Such an isolator/circulator device is a directional device, a high value-added device which is used in a transport communication system, a satellite communication system and a millimeter wave because the frequency modulation control is easy.
The conventional art for such an isolator/circulator will be explained by means of the attached drawings as follows.
FIG. 1(a)(1) is a structural view of a conventional microstrip/stripline isolator/circulator.
FIG. 1(a)(2) is a sectional view of a conventional microstrip/stripline isolator/circulator, and FIG. 1b is a plane view of FIG. 1a.
As shown FIGS. 1(a)(1) and 1(a)(2), a conventional 3-terminal microstrip/stripline isolator/circulator includes a microstrip/stripline pattern 104 on the upper portion of a ferrite substrate 102 and on the lower portion of the ferrite substrate 102, an upper permanent magnet 103a over the upper portion of the ferrite substrate 102 and a lower permanent magnet 103b under the lower portion of the ferrite substrate 102, and a thin iron plate 108 between the upper permanent magnet 103a and a microstrip/stripline 104. In the case of microstrip 104, a thin dielectric is inserted between microstrip 104 and the thin iron plate 108.
As shown in FIG. 1b, an electrode pattern of the microstrip/stripline 104 comprises a circular resonator 104 resonating on a constant frequency in the central portion, a first electrode 105a and a second electrode 105b and a third electrode 105c being achieved symmetrically to each other in the circumference of the circular resonator 104 and 3 electrode terminals which connect an external circuit with the circular resonator 104 through the respective transfer tracks 106a, 106b, 106, and a 50.OMEGA. load resistence being connected to the third electrode 105c in the case of an isolator.
In such a microstrip/stripline isolator/circulator, a signal of the external circuit is transferred from the first electrode 105a composed of a first port to the second electrode 105b composed of a second port, similarly from the second electrode 105b to the third electrode 105c, and from the third electrode 105c to the first electrode 105a in a clockwise direction by means of non-reversible characteristic of the microstrip/stripline 104 formation on the ferrite substrate 102, the upper permanent magnet 103a and lower permanent magnet 103b. In the case of an isolator, the signal is transferred from the second electrode 105b to the third electrode 105c, and the signal is extinguished through the load resistance. That is, since the signal is transferred from the first electrode 105a to the second electrode 105b, and not from the second electrode 105b to the first electrode 105a, it performs the action of an isolator. Then, the signal transfer direction can be set in the counterclockwise direction.
However, in a conventional microstrip/stripline isolator/circulator using such a circular resonator 104, the size of the circular resonator 104 is inversely proportional to a resonator frequency, however, there is a problem that it is difficult to fabricate a miniature isolator/circulator due to limitations in reducing the size of the circular resonator 104 to be used for UHF for a transfer communication or personal communication.
Accordingly, there has been active pursuit of study for developing an isolator/circulator having a microstrip/stripline comprising a miniaturized isolator/circulator to be efficiently used for UHF for a transfer communication system or personal communication system according to the miniature trend and communicative system development. FIG. 2 illustrates a form of a typical conventional microstrip/stripline pattern related to this pursuit.
FIG. 2 illustrates another pattern form of a microstrip/stripline to a convention isolator/circulator.
As shown in FIG. 2, a microstrip/stripline of a conventional isolator/circulator is composed of a circular resonator 204 formed in the central portion as an electrode pattern, three slots 207 formed in the central direction from a circumference of the circular resonator 204 to control a magnet coupling quantity, a first electrode 205a, a second electrode 205b and a third electrode 205c constituting three symmetric ports which connect the resonator 204 with external circuit in the circumference thereof through the respective transfer tracks 206a, 206b, 206c, and a load resistence.
In a conventional microstrip/stripline isolator/circulator constructed as described above, since a magnet wall is formed in the slot 207 of the microstrip/stripline, the length of the slot 207 in the same frequency can be controlled compared to the microstrip/stripline shown in FIG. 1, and as a result, there can be performed a miniaturization of the isolator/circulator. However, the magnet wall formed on the resonator is used. The size of the magnet used is greater than that of the resonator. A circuit should be connected to the external in order to expand the bandwidth. Accordingly, if the bandwidth is expanded, the isolator/circulator size increases, thus prohibiting reduced size in fabrication thereof and increasing manufacture costs. In addition, there is a limit to reducing an insertion loss with regards to the characteristic thereof.
Since there is applied a magnet to the size of the resonator formed on the ferrite, ferromagnetic resonance line width (.DELTA.H) of loss portion of magnetic material is related by the resonator size, therefore, to minimize the low insertion loss.
FIG. 3 shows another pattern form of a microstrip/stripline for a conventional isolator/circulator.
As shown in FIG. 3, a microstrip/stripline of a conventional isolator/circulator is composed of a triangular resonator 304 formed in the central portion as an electrode pattern, three slots 307 formed in the central direction from the respective side of the triangular resonator 304 to control a magnetic coupling quantity, open .lambda./4 ring type coupling transfer tracks 306a, 306b and 306c, on a ring type dielectric material 308 around the resonator 304, a first electrode 305a, a second electrode 305b and a third electrode 305c constituting symmetric ports to connect the external circuit with open .lambda./4 ring type coupling transfer tracks, and a load resistence. The open .lambda./4 ring type coupling transfer tracks 306a, 306b, 306c, of each terminal case magnetic coupling, the groove of the triangular resonator 304 cause the magnetic coupling. Due to these magnetic couplings, in order to perform a miniaturization of an isolator/circulator, since the respective terminal of open .lambda./4 ring type coupling transfer tracks and the respective terminals 305a, 305b, 305c cause the magnetic coupling, the triangular resonator portion of open .lambda./4 ring type coupling transfer tracks 306a, 306b, 306c and the triangular resonator 304 cause the magnetic coupling, impedance matching is preferable. In addition, it is preferable to simplify manufacturing. However, there is a limit for reducing the size because of using the magnetic coupling as in FIG. 2.